Brake-by-Steer Concept

1Brake-by-Steer Concept

20-04-23

Challenge the future

DelftUniversity ofTechnology

Brake-by-Steer ConceptSteer-by-wire application with independently actuated wheels used for stopping a vehicle

Bas Jansen 25-03-2010

Master Thesis PresentationDepartment of Precision and Microsystems Engineering


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Content1. Introduction

- SKF

- Drive-by-wire

- Brake-by-steer concept

2. Modeling the Brake-by-Steer system- Tire model

- Vehicle model

- Brake-by-steer cases

3. Implementation on a Go-Kart- Go-kart introduction

- Design Implementations

4. Test Results - Braking performance

- Lateral behavior

5. Conclusion & Recommendations


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1.Introduction


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IntroductionSKF - Svenska Kullagerfabriken AB


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Introduction

SKF European Research CentreNieuwegein

SKF - Svenska Kullagerfabriken AB


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Introduction

Conventional steering system

Steer-by-wire with independently actuated wheels

What is Steer-by-WireSteering wheel

Steering shaft

Rack & Pinion

Steering ControllerSensor & actuator

Sensor & actuator

Data transport


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Introduction

Replace hydraulic brake system with an individually electrically actuated brake system

What is Brake-by-WireElectro mechanical braking actuators

Braking controller

Brake pedal & sensor

Data transport


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IntroductionWhy By-Wire

Modular design provides design freedom, reduces weight and requires less space

Personalized and adaptive driving experience by varying control settings

Increased safety potential in combination with intelligent vehicle safety systems


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Introduction Safety challenge for By-Wire

Increase safety level:• Implemented redundant components

• Assign secondary function to initial primary function of a sub system

• Steer by uneven distributed brake force• Brake-by-steer concept

Primary systems with redundant back-up systems


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Introduction

Research Question:

Is it possible to stop a vehicle with the brake-by-steer concept and how does

this influence the steering controllability?

Brake-by-Steer concept Position the front wheels such that

they generate a braking force


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2.Modeling the Brake-by-Steer

system


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Brake-by-Steer Modeling

Model build-up:• Tire model • Vehicle (kart) model• Brake-by-Steer cases

Model construction

tireF

Width

Lengthm, I

vehicleV

tireV


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Tire behavior:• No resistance force in longitudinal direction (x)• Resistance force in lateral direction (y)

Slip angle:The angle between tire’s direction of travel (V) and the direction towards which it is pointing (x)

Tire modeling

tanv

u

, ,

x y Tire coordinatesu v Tire velocitiesV Tire velocity vector

Slip angle

,y v

,x u

V


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0 5 10 15 20 25 300

0.2

0.4

0.6

0.8

1

Slip angle (deg)

Late

ral t

ire f

orce

(N

)Brake-by-Steer Modeling Tire modeling

Slip angle

Late

ral T

ire F

orc

e

, ,

Lat

x y Tire coordinatesu v Tire velocitiesV Tire velocity vector

Slip angleF Lateral tire force

C

1

, for , for

sin tan

saturateLat

saturate saturate

lat

CF

F

F d c b

lateral tireF

,y v

,x u

V


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Brake-by-Steer Modeling Vehicle Model

V

,y v

,x u

lateral tireF

X

Y

Z

Fu vr

mF

v urm

Mr

I

X

Y

Vehicle equations of motion

m, IV

u

v

cos

sinX lateral tire

Y lateral tire

F F

F F

X

Y

Tricycle model


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Brake-by-Steer Modeling Brake-by-Steer cases

Symmetric Asymmetric

Toe-in

Toe-

out

Steering angle Left S

teer

ing

ang

le R

ight

Toe-out

Toe-in

Toe-out

Toe-in

Steady state straight line driving brake force

Bra

ke f

orc

e [

N]


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tireF

X leftFtireF X rightF

tireF

X right X leftvehicle t F FM

Steering to the right results in vehicle moment to the left

Steering to the right results in vehicle moment to the right

Toe-in steer to the right Toe-out steer to the right

t

X right X leftvehicle t F FM

X leftF X rightF

t

Effect of longitudinal vehicle force for vehicle heading


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tireF

Y leftFtireF Y rightF

tireF

Y Y left Y rightF FF

Steering to the right results in lateral vehicle force to the left

Steering to the right results in lateral vehicle force to the left

Toe-in steer to the right Toe-out steer to the right

X leftF X rightF

Y Y right Y leftF FF

Effect of lateral vehicle force for vehicle heading


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Brake-by-Steer Modeling Theoretical Results – Lateral Behavior

Steering angle Left

Ste

erin

g an

gle

Rig

ht

Su

mm

atio

n L

ate

ral V

eh

icle

Fo

rce

[N

] Symmetric toe equilibrium

Asymmetric toe equilibrium

Toe-out

Toe-in

There is no asymmetric toe-out equilibrium line


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3.Implementation on a Go-Kart


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Implementation on a Go-Kart Go-Kart Introduction

Kart specific features:• No individual wheel suspension• Flexible tube frame acts as suspension• Fixed rear axle • Caster angle and kingpin inclination

Caster angle

Kingpin inclination

Caster angle

Left tire side view

Rotational path

Remove mechanical linkage


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Implementation on a Go-Kart

Steering WheelElectromechanical Modifications

Steering wheel actuator

Steering wheel angle sensorSteering shaft

Toe handle

• Absolute magnetic encoder measures steering angle• DC motor provides force feedback sense • Toe levers measure toe angle setpoints


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Implementation on a Go-Kart Electromechanical ModificationsWheels

Extension brackets

Motor + gear

Absolute angle sensor

Encoders

• DC motor positions the wheels• Encoder used as control position signal • Absolute angle sensor used homing during initialization

Stub axle


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Implementation on a Go-Kart Control algorithm

CController +/-

K

Feedback position control for wheel positions

Force feedback to steering wheel

Toe mode selection

Motor currentsForce


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Implementation on a Go-Kart Control algorithm

CController

K0

kartV

+/-

Mimic steering torque with speed dependent return to center torque

Feedback position control for wheel positions

Toe mode selection


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Implementation on a Go-Kart Implemented design

Electronics

Batteries

Left wheel actuation

Steering wheel actuation

Velocity sensor


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4.Test Cases and Results


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Test cases & Results

• Braking performance of the brake-by-steer concept • Lateral vehicle behavior during brake-by-steer maneuver

Test cases

Test track at SKF ERC Nieuwegein


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Test cases & Results Results – Braking Performance

0 20 40 60 80 100 120 140 160 180-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

Effective toe angle (deg)

Bra

ke f

orce

(kN

)

Toe in

Toe outOne wheel

Theoreticle data

,sin itire saturatebrake

i left rightF F

Theoretical maximum:

1.5 kN

0 1 2 3 4 5 6 7-6

-4

-2

0

2

4

6

8

10

Time (sec)

(Var

ious

)

Velocity (m/s)

Acceleration (m/s2)

Brake Force (kN)


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Test cases & Results Results – Lateral behavior

Calculated driven path for symmetric toe-in (30º) with steering offset of 2, 4, 6, 8 degrees to the right

0 0.5 1 1.5 2 2.5 3 3.5

-30

-20

-10

0

10

20

30

40

0 0.5 1 1.5 2 2.5 3 3.5-10

-5

0

5

Path for L: 38 (rad),

R: -22 (deg),

Velocity: 5 [m/s], C1: 850, C2: 1200

Time (sec)

var

ious

u (m/s)

v (m/s)r (deg/s)

0 1 2 3 4 5 6 7 8 9

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

X [m]

Y [

m]

Slip angles

Velocities


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0 0.2 0.4 0.6 0.8 1 1.2 1.4

-60

-40

-20

0

20

40

60

80

100

Time (sec)

Slip

ang

le (

deg)

Right

LeftRear

0 0.2 0.4 0.6 0.8 1 1.2 1.4-14

-12

-10

-8

-6

-4

-2

0

2

4

6

Path for L: -52 (rad),

R: 68 (deg),

Velocity: 5 [m/s], C1: 850, C2: 1200

Time (sec)

var

ious

u (m/s)

v (m/s)r (deg/s)

Test cases & Results Results – Lateral behavior

Calculated driven path for symmetric toe-out (60º) with steering offset of 2, 4, 6, 8 degrees to the right

Slip angles

Velocities

0 0.5 1 1.5 2 2.5 3

-0.25

-0.2

-0.15

-0.1

-0.05

0

X [m]

Y [

m]


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5.Conclusions & Recommendations


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Conclusions & Recommendations

Brake-by-steer concept can back-up failing brakes with a reduced braking performance (~50%).

Lateral behavior changes drastically and ranges of inverted steering occur. These make the vehicle uncontrollable for the driver.

Conclusions Brake-by-Steer Concept


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Symmetric Asymmetric

Toe-in

Good braking capability

Good steering capability

(although inverted)

Not effective braking


Toe-out

Good braking capability


(although partly inverted)

Not effective braking

Impossible to drive straight

Conclusions Toe-modes

Theory and practice differ on effectiveness of toe modes due to due to caster angle and kingpin inclination induced roll motion. The kart tire that is turned out the most gains vertical axle load and dictates the lateral behavior of the vehicle.


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Conclusions & Recommendations Recommendations Brake-by-Steer Concept

Before the brake-by-steer concept can be applied in cars, the relation between steering angle and vehicle heading must be restored. Calculate how to position the wheels to generate a brake force and follow expected steering input according toe strategy.

Controller Wheel

actuators

Steering angleBrake pedal

...

Velocity

Lateral accelerations

To create this model the presented conceptual model needs to be extended and validated on a car in stead of a go-kart


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Thank you for your attention

Questions?


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Implementation on a Go-Kart Steering system design requirements

Strain gages

Angle sensor

Velocity sensor

Performance requirements: • Wheel steering rate typical 80 º/s • Steering frequency typical 1 Hz (amp = ~10 deg)• Steering torque at wheels

• Nominal 8 Nm• Peak 50 Nm

Measured braking performance• Braking Force 1,2 kN


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-80 -60 -40 -20 0 20 40 60 80-1000

-800

-600

-400

-200

0

200

400

600

800

1000

Slip angle (deg)

Late

ral f

orce

(N

)

A0

A1

B0

B1

coslateral vehicle lateral tire

F F

Late

ral V

ehi

cle

For

ce [

N]

Slip angle

Inverted steering occurs at symmetric toe mode for > saturate

A1

Brake-by-Steer cases – Vehicle controllability


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The hub motor (2) is located inside the wheel rim (1).

The electronic wedge brake (3) uses pads driven by electric motors.

An active suspension (4) and electronic steering (5) replace conventional hydraulic systems.

Siemens VDO eCornerBACKUP


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tireF

X vehicle leftF

X vehicle leftF

tireF

tireF

tireF

X vehicle rightF

X vehicle rightF

BACKUP

Date post:	03-Jan-2016
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Brake-by-Steer Concept

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